Logical circuit

ABSTRACT

A logical circuit receives first and second input signals in which a period of a first logic level partially overlaps, and outputs first and second output signals in which a period of the first logic level does not overlap. The logical circuit comprises a first unit which changes a phase of the first output signal from a second logic level to the first logic level when a change of the first input signal from the second logic level to the first logic level is detected. A second unit changes a phase of the second output signal from the first logic level to the second logic level when the second input signal is detected as being at the first logic level at a time of detection of the change of the first input signal.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation Application, which claims the benefit of pendingU.S. patent application Ser. No. 11/042,335 filed Jan. 26, 2005, whichin turn is a Continuation Application of International Application No.PCT/JP2003/03030, filed on Mar. 13, 2003. The disclosure of the priorapplication is hereby incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a logical circuit which is carried on asemiconductor device and outputs the output signals in which the periodof the logic level (H) does not overlap even when the logical circuitreceives the input signals in which the period of the logic level (H)partially overlaps.

2. Description of the Related Art

As a logical circuit which outputs the signals in which the period ofthe logic level (H) does not overlap, the EX-OR (exclusive-or) circuitis well known.

In a case of the EX-OR circuit, the output signal will be influenced byone of the input signals at the time of rising of the other of the inputsignals.

This is a significant problem for a certain circuit, such as a DLL(delay-locked loop) circuit in which the timing of rising of the signalsis important. In a semiconductor device carrying the circuit whichoperates at a high speed synchronized with the clock signal, a variationof phase in the clock signal may arise due to signal transmission delayor the like.

When a logical circuit which outputs the signals in which the period ofthe logic level (H) does not overlap is added to the semiconductordevice and used together in order to reduce such phase variation of theclock signal as much as possible, consideration must be taken on theconformity of the logical circuit with the circuit in which the timingof rising of the signals is important.

For this reason, it is demanded to provide a logical circuit whichoutputs the signals in which the period of the logic level (H) does notoverlap and can be used suitably with the circuit, such as the DLLcircuit in which the timing of rising of the signals is important, insuch a manner that rising of the signal is not affected but falling ofthe signal is affected.

FIG. 1A shows an example of the conventional logical circuit. FIG. 1Bshows the signal waveform of the input signals A and B to the logicalcircuit of FIG. 1A, and the output signals C and D from the logicalcircuit.

The logical circuit of FIG. 1A is a general EX-OR circuit that outputsthe signals in which the period of the logic level (H) does not overlap.

The EX-OR circuit comprises the inverter 1, the inverter 2, the inverter3, the inverter 4, the NOR gate 5, and the NOR gate 6.

In the EX-OR circuit of FIG. 1A, the input signal A is inputted to theinverter 1, and the input signal B is inputted to the inverter 2. Theoutput of the inverter 1 is inputted to one input of the NOR gate 5while it is inputted to the inverter 3. The output of the inverter 2 isinputted to one input of the NOR gate 6 while it is inputted to theinverter 4.

The output of the inverter 3 is inputted to the other input of the NORgate 6. The output of the inverter 4 is inputted to the other input ofthe NOR gate 5. The NOR gate 5 receives the outputs from the inverter 1and the inverter 4 and outputs the output signal C, and the NOR gate 6receives the outputs from the inverter 2 and the inverter 3 and outputsthe output signal D.

Consideration will now be taken to the case where the phase of the inputsignal A and the input signal B is shifted somewhat with reference toFIG. 1B.

The input signal A and the input signal B are, for example, the twoclock signals which have different phases.

To these input clock signals, the variation in the phase may arise dueto transmission delay of the clock signals in the semiconductor devicecarrying the circuit which operates at the high speed synchronized withthe clock signals.

As shown in FIG. 1B, when the input signal B is at the logic level (L)at the instant the input signal A has changed from the logic level (L)to the logic level (H) (the time of rising), the phase of the inputsignal A transfers to the phase the output signal C as it is.

However, when the input signal B is at the logic level (H) at the timeof rising of the input signal A, the output signal C still remains atthe logic level (L).

When the input signal B changes from the logic level (H) to the logiclevel (L), the phase of the input signal A transfers to the phase of theoutput signal C for the first time.

That is, the time of rising of the input signal A will be delayed untilthe phase of the input signal B changes to the logic level (L), and thenthe output signal C will be outputted.

In other words, the EX-OR circuit of FIG. 1A operates such that theportion in which the logic level (H) of the input signal A overlaps withthe input signal B is deleted from the portion in which the phase ischanged from the logic level (L) to the logic level (H), and theoverlapping of the logic level (H) of the output signal is eliminated.

However, when the method of the EX-OR circuit is applied to the circuitlike the DLL circuit in which the timing of rising is important, thedelay of the timing of rising is affected by the counterpart signal, andexcessive delay time (loss) may arise, which will become the factorwhich worsens the underflow of the DLL circuit (which indicates thecircuit performance with the delay minimum value).

Moreover, FIG. 2 is a diagram for explaining operation of theconventional logical circuit of FIG. 1A when the phase shift of theinput signals occurs at intervals of the period of some cycles.

As shown in FIG. 2, when a phase shift of the input signal B to theinput signal A occurs at intervals of some cycles, rather than the casewhere the phase shift occurs for every cycle, the conventional logicalcircuit may also cause the deviation of the phase of the input signal A.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved logicalcircuit in which the above-described problems are eliminated.

Another object of the present invention is to provide a logical circuitwhich outputs the signals in which the period of the logic level (H)does not overlap and can be suitably used with a DLL circuit or the likein which the timing of rising is important, such that rising of thesignals is not affected but falling of the signals is affected,

In order to achieve the above-mentioned objects, the present inventionprovides a logical circuit which receives first and second input signalsin which a period of a first logic level partially overlaps, and outputsfirst and second output signals in which a period of the first logiclevel does not overlap, the logical circuit comprising: a first unitwhich changes a phase of the first output signal from a second logiclevel to the first logic level when a change of the first input signalfrom the second logic level to the first logic level is detected; and asecond unit which changes a phase of the second output signal from thefirst logic level to the second logic level when the second input signalis detected as being at the first logic level at a time of detection ofthe change of the first input signal.

As a logical circuit in which the period of the logic level (H) of thetwo output signals does not overlap, in the case of EX-OR circuit, theoutput signals will be influenced when one of the input signals is atthe logic level (H) at a time of rising of the other input signal.

In the logical circuit of the present invention, rising of the signalsis not influenced by the phase of the counterpart input signal.Therefore, according to the logical circuit of the present invention, itis possible to output the output signals in which the period of thelogic level (H) does not overlap, without being influenced by either ofthe input signals at the time of rising of the counterpart input signal.

By applying the logical circuit of the present invention to the circuitlike the DLL circuit in which the timing of rising of the signals isimportant, it is possible that outputting the signals in which theperiod of the logic level (H) does not overlap be guaranteed andexcessive delay time be shortened, without being influenced due tofluctuation of the input signals at the time of rising of one of theinput signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

FIG. 1A is a circuit diagram showing the conventional logical circuit.

FIG. 1B is a waveform diagram showing the signal waveform of the inputsignals A and B to the logical circuit of FIG. 1A, and the outputsignals C and D.

FIG. 2 is a diagram for explaining operation of the logical circuit ofFIG. 1A.

FIG. 3 is a circuit diagram showing the logical circuit in oneembodiment of the invention.

FIG. 4 is a block diagram showing an example of composition of thesemiconductor device using the EX-OR circuit in which outputting thefirst and second signals in which the period of the logic level (H) doesnot overlap is needed.

FIG. 5 is a circuit diagram showing an example of the circuit in FIG. 4in which the signals in which the period of the logic level (H) does notoverlap are needed.

FIG. 6A is a waveform diagram showing the signal waveform of the inputsignals A and B to the logical circuit of FIG. 3, and the output signalsC and D.

FIG. 6B is a diagram for explaining operation of the logical circuit ofFIG. 3 at the time of outputting the output signal C to the inputsignals A and B.

FIG. 6C is a diagram for explaining operation of the logical circuit ofFIG. 3 at the time of outputting the output signal D to the inputsignals A and B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A description will now be given of the preferred embodiments of theinvention with reference to the accompanying drawings.

FIG. 3 shows the logical circuit in one embodiment of the presentinvention.

In the logical circuit of FIG. 3, the circuit elements of the upper-sidecircuit block configured to output the output signal C and the circuitelements of the lower-side circuit block configured to output the outputsignal D are arranged symmetrically.

The upper-side circuit block of the logical circuit of FIG. 3 comprisesthe output unit 51A which outputs the output signal C, thecircuit-element group 52A which transmits the input signal B, and thecircuit-element group 53A which controls the transmission line (path) ofthe circuit-element group 52A based on the logic information of theinput signal A and the counterpart input signal B.

The circuit-element group 52A and the circuit-element group 53A functionas a state holding unit which holds, when the phase of the input signalA and the phase of the input signal B are set to the logic level (H)simultaneously, the state of the input signal B immediately precedingthe setting.

Similarly, the lower-side circuit block of the logical circuit of FIG. 3comprises the output unit 51B which outputs the output signal D, thecircuit-element group 52B which transmits the input signal A, and thecircuit-element group 53B which controls the transmission line (path) ofthe circuit-element group 52B by using the logic information of theinput signal B and the counterpart input signal A.

The circuit-element group 52B and the circuit-element group 53B functionas a state holding unit which holds, when the phase of the input signalA and the phase of the input signal B are set to the logic level (H)simultaneously, the state of the input signal A immediately precedingthe setting.

As mentioned above, the circuit elements of the upper-side circuit blockand the circuit elements of the lower-side circuit block in the logicalcircuit of this embodiment are the same, and, for the sake ofconvenience of description, only the circuit elements of the upper-sidecircuit block will be explained in the following, and a description ofthe lower-side circuit block will be omitted.

The circuit-element group 51A comprises the inverter 21 to which theinput signal A is inputted, and the NOR gate 22 to which the output ofthe inverter 21 and the output of the circuit-element group 52A areinputted.

The circuit-element group 53A comprises the NAND gate 32 to which theinput signal A and the input signal B are inputted, the transistor 33,and the transistor 34.

The transistor 33 has the gate to which the output of the NAND gate 32is inputted, and the source-drain path one end of which is connectedwith the power-supply voltage line and the other end of which isconnected with the source-drain path of the transistor 28.

The transistor 34 has the gate to which the output of the NAND gate 32is inputted, and the source-drain path one end of which is grounded andthe other end of which is connected with the output of thecircuit-element group 52A.

The circuit-element group 52A comprises the inverter 23 to which theinput signal B is inputted, the inverter 24 to which the output of theinverter 23 is inputted, the transistor 25, the transistor 26, thetransistor 27, the transistor 28, the inverter 29, the transistor 30,and the transistor 31.

The transistor 25 and the transistor 26 have the respective source-drainpaths which are connected with each other, one of the source-drain pathsis connected to the output of the inverter 24, and the other of thesource-drain paths is connected to the input of the inverter 29.

The transistor 25 has the gate to which the output of the NAND gate 32is inputted. The transistor 26 has the gate to which the output of theinverter 35 is inputted.

Moreover, in the circuit-element group 52A, the transistor 28 has thegate to which the output of the inverter 29 is inputted, and thesource-drain path one end of which is connected with the source-drainpath of the transistor 33, and the other end of which is connected withthe source-drain path of the transistor 27.

The transistor 27 has the gate to which the output of the inverter 29 isinputted, and the source-drain path one end of which is connected withthe source-drain path of the transistor 36, and the other end of whichis connected with the source-drain path of the transistor 28.

Moreover, in the circuit-element group 52A, the inverter 29 has theinput which is connected with the source-drain path of the transistors27 and 28, and the output which is connected with the source-drain pathof the transistors 30 and 31.

The transistor 30 and the transistor 31 have the respective source-drainpaths which are connected with each other, one of the source-drain pathsis connected to the output of the inverter 29, and the other of thesource-drain paths is connected to the source-drain path of thetransistor 34.

The transistor 30 has the gate to which the output of the NAND gate 32is inputted. The transistor 31 has the gate to which the output of theinverter 35 is inputted.

Furthermore, the upper-side circuit block of the logical circuit of FIG.3 comprises the inverter 35 to which the output of the NAND gate 32 isinputted, and the transistor 36. The transistor 36 has the gate wherethe output of the inverter 35 is inputted, and the source-drain path oneend of which is connected with the source-drain path of the transistor27, and the other end of which is grounded.

As mentioned above, the lower-side circuit block of the logical circuitof FIG. 3 has the composition which is the same as the upper-sidecircuit block thereof. The lower-side circuit block comprises the outputunit 51B which outputs the output signal D, the circuit-element group52B which transmits the input signal A, and the circuit-element group53B which controls the transmission line (path) of the circuit-elementgroup 52B based on the logic information of the input signal B and thecounterpart input signal A.

FIG. 6A shows the signal waveform of the input signals A and B to thelogical circuit of FIG. 3, and the output signals C and D. FIG. 6B is adiagram for explaining operation of the logical circuit of FIG. 3 at thetime of outputting the output signal C responsive to the input signals Aand B. FIG. 6C is a diagram for explaining operation of the logicalcircuit of FIG. 3 at the time of outputting the output signal Dresponsive to the input signals A and B.

In FIG. 6B and FIG. 6C, t1, t2, t3, t4, and t5 respectively indicate theinstants which are the same as the corresponding timings of theinput/output signals in the signal waveform of FIG. 6A which aredesignated by the same reference numerals. In FIG. 6B, a, b, c, d, e, f,and g respectively indicate the nodes which are the same as thecorresponding nodes in the upper-side circuit block of the logicalcircuit of FIG. 3 which are designated by the same reference numerals.

Moreover, in FIG. 6C, h, i, j, k, l, m, and n respectively indicate thenodes which are the same as corresponding nodes in the lower-sidecircuit block of the logical circuit of FIG. 3 which are designated bythe same reference numerals.

As is apparent from the signal waveform of FIG. 6A, at the time of t1,the input signal A is at the logic level (L), and the input signal B isat the logic level (H).

At the time of t2, the input signal A rises to the logic level (H), andboth the phase of the input signal A and the phase of the input signal Bare set to the logic level (H) simultaneously.

At the time of t3, the input signal B falls to the logic level (L), andthe input signal A still remains at the logic level (H).

At the time of t4, the input signal A falls to the logic level (L), andthe input signal B still remains at the logic level (L).

At the time of t5, the input signal B rises to the logic level (H), andthe input signal A still remains at the logic level (L).

As shown in FIG. 6A, when the phase of the input signal A is changedfrom the logic level (L) to the logic level (H) (at the time of t2), thelogical circuit of FIG. 3 functions to transfer the phase of the inputsignal A to the phase of the output signal C as it is, even if thecounterpart input signal B is still at the logic level (H).

On the other hand, when the phase of the counterpart input signal B ischanged from the logic level (H) to the logic level (L) (at the time oft3), the output signal D is still at the logic level (L). And the phaseof the input signal B is not transferred to the phase of the outputsignal D. The position of falling of the output signal relative to theinput signal will be shifted.

As mentioned above, in the EX-OR circuit of FIG. 1A, rising of one inputsignal is influenced by the counterpart input signal and falling is notinfluenced. On the other hand, in the logical circuit of the presentinvention, rising is not influenced by the counterpart input signal, butfalling is influenced by the state of the counterpart input signal.

According to the logical circuit of the present invention, excessivedelay time can be shortened without being influenced due to fluctuationof the input signals at the time of rising of one of the input signals.When it is applied to the circuit like the DLL circuit in which thetiming of rising is important, the logical circuit of the invention isvery useful because the two output signals in which the period of thelogic level (H) does not overlap are outputted while rising of one ofthe input signals is not influenced by the counterpart input signal.

FIG. 4 shows an example of composition of the semiconductor device usingthe EX-OR circuit, which incorporates the circuit which requiresreceiving the incoming signals in which the period of the logic level(H) does not overlap.

As shown in FIG. 4, the semiconductor device of this embodimentcomprises the DLL delay circuit group 61, the DLL comparator and controlcircuits 62, the EX-OR circuit 63, and the circuit 64 which needsreceiving the incoming signals in which the period of the logic level(H) does not overlap.

A description of the circuit 64 which needs receiving the incomingsignals in which the period of the logic level (H) does not overlap willbe given later with reference to FIG. 5.

In the semiconductor device of FIG. 4, the EX-OR circuit 63 has thecircuit configuration that is the same as that of the logical circuit ofFIG. 1A, and it is inserted in the circuit configuration including thegeneral DLL circuit.

FIG. 5 shows an example of the circuit 64 which needs receiving theincoming signals in which the period of the logic level (H) does notoverlap, for use in the semiconductor device of FIG. 4.

The outputs of the circuit of FIG. 5 are arranged in the wired-orconnection. The circuit of FIG. 5 comprises the inverter 71, theinverter 72, the transistor 73, the transistor 74, the transistor 75,the transistor 76, the inverter 77, the inverter 78, and the inverter79.

The 0-degree clock signal is inputted to the gate of the transistor 73,and inputted to the input of the inverter 71. The signal which is set bythe inversion of the output of the inverter 71 is inputted to the gateof the transistor 74.

The respective source-drain paths of the transistors 73 and 74 areconnected with each other, and the data 1 for the 0-degree clock inputis inputted to one of the source-drain paths, and it is transmitted tothe output terminal of the circuit of FIG. 5 via the other of thesource-drain paths.

The 180-degree clock signal is inputted to the gate of the transistor75, and inputted to the input of the inverter 72. The signal which isset by the inversion of the output of the inverter 72 is inputted to thegate of the transistor 76.

The respective source-drain paths of the transistors 75 and 76 areconnected with each other, and the data 2 for the 180-degree clock inputis inputted to one of the source-drain paths, and it is transmitted tothe output terminal of the circuit of FIG. 5 via the other of thesource-drain paths.

In the circuit of FIG. 5, the data bus is divided into two: one for the0-degree clock input, and the other for the 180-degree clock input.

From the output terminal of the circuit of FIG. 5, the data are seriallyoutputted in accordance with the 0-degree clock signal and the180-degree clock signal.

Namely, the circuit of FIG. 5 is the parallel-serial conversion circuitwhich receives the data 1 for the 0-degree clock input and the data 2for the 180-degree clock input in parallel, and outputs the dataserially in accordance with the 0-degree clock signal and the 180-degreeclock signal.

In the circuit of FIG. 5, if the 0-degree clock signal and the180-degree clock signal, which are provided to perform the outputcontrol, indicate the logic level (H) simultaneously, the data willcollide depending on the state of the data.

For this reason, it is necessary to secure that the logic level (H) ofthe signals does not overlap, and therefore, the EX-OR circuit 63 isinserted in the semiconductor device as shown in FIG. 4.

However, in the conventional EX-OR circuit 63, the transitional portionof the input clock signal from the logic level (L) to the logic level(H) is deleted in order to secure that the logic level (H) of thesignals does not overlap, and even though the clock signals with thephases locked by the DLL circuit are outputted, the deletion of thetransitional portion of the input clock signal by the EX-OR circuit 63will cause the variation of the clock phase to arise.

It is satisfactory if there is no overlapping of the period of the logiclevel (H) between the input clock signals before being inputted to theEX-OR circuit 63. However, there are some influences, such as thefluctuation of the pulse width of the clock signals in the transmissionpath of the DLL delay circuit group 61, and the fluctuation of the delayposition. Hence, it is difficult to guarantee that the period of thelogic level (H) in the input clock signals does not overlap at all.

For this reason, the removal of the clock signal portion will occur inthe EX-OR circuit 63, and this will cause the variation of operation ofthe semiconductor device.

To obviate the problem, by using the logical circuit of FIG. 3 in thesemiconductor device of FIG. 4 instead of the EX-OR circuit 63, it ispossible that the removal of the transitional portion from the logiclevel (L) to the logic level (H) of the input signal does not occur, asshown in FIG. 6A, which makes it possible to suppress the variation ofoperation.

According to the logical circuit of the present invention, it ispossible to output the output signals in which the period of the logiclevel (H) does not overlap, without being influenced by either of theinput signals at the time of rising of the counterpart input signal.

By applying the logical circuit of the present invention to the circuitlike the DLL circuit in which the timing of rising of the signals isimportant, it is possible that outputting the signals in which theperiod of the logic level (H) does not overlap be guaranteed andexcessive delay time be shortened, without being influenced due tofluctuation of the input signals at the time of rising of one of theinput signals.

Moreover, since the factor which worsens the underflow of the DLLcircuit as in the conventional logical circuit does not arise, thelogical circuit of the present invention is effective as a logicalcircuit which outputs the signals in which the period of the logic level(H) does not overlap.

The present invention is not limited to the above-described embodiments,and variations and modifications may be made without departing from thescope of the present invention.

1. A semicondutor chip comprising: a first unit coupled to receive atleast a first input clock signal and a second input clock signal, andoutput a first output clock signal; a second unit coupled to receive thefirst input clock signal and the second input clock signal, and output asecond output clock signal that has periodically the first logic leveland the second logic level; a first transfer gate which receives a firstdata, and transmits the first data to a data bus in response to a firstlogic level of the first output clock signal; a second transfer gatewhich receives a second data, and transmits the second data to the databus in response to the first logic level of the second output clocksignal; wherein the first unit changes the first output clock signalfrom a second logic level to the first logic level when a change of thefirst input clock signal from the second logic level to the first logiclevel is detected, and the second unit changes the first output clocksignal from the first logic level to the second logic level when thesecond input signal is detected as being at the first logic level at atime of detection of the change of the first input signal.
 2. Asemiconductor chip according to claim 1, wherein the first input clocksignal, the second input clock signal and the first output clock signalhave periodically a first logic level or a second logic level and aperiod of the first logic level of the second output clock signal doesnot overlap a period of the first logic level of the first output clocksignal.
 3. A semiconductor chip according to claim 1, wherein the firstinput clock signal and the second input clock signal have mutuallyshifted phases.
 4. A semiconductor chip according to claim 1, whereinthe first data and the second data are alternately outputted in serial.5. A semiconductor chip according to claim 4, further comprising: alatch circuit that latches one of the first data and the second data. 6.A semicondutor chip according to claim 1, wherein the first input clocksignal and the second input clock signal are supplied from a DLL DelayCircuit.
 7. A semiconductor chip according to claim 1, wherein a periodof the first logic level of the first input clock signal partiallyoverlaps with that of the first logic level of the first input clock. 8.A semiconductor chip according to claim 1, wherein the second unitchanges the first output clock signal from the first logic level to thesecond logic level when the second input signal is detected as being atthe first logic level at a time of detection of the change of the firstinput signal and when the first logic level of the first input clocksignal is detected at a time of detection of the change of the secondinput clock signal form the second logic level to the first logic level.9. A semiconductor chip comprising: a first unit coupled to receive afirst input clock signal and a second input clock signal and output afirst output clock signal; a second unit coupled to receive the firstinput clock signal and the second input clock signal and output a secondoutput clock signal; a circuit coupled to receives a first data and asecond data and outputs the first data and the second data in serial inresponse to the first output signal and the second output signal, thecircuit is arranged wired-or connection; wherein the first unit changesthe first output clock signal from the second logic level to the firstlogic level when a change of the first input clock signal from thesecond logic level to the first logic level is detected, and the secondunit changes the first output clock signal from the first logic level tothe second logic level when the second input signal is detected as beingat the first logic level at a time of detection of the change of thefirst input signal.
 10. A semicondutor chip according to claim 8,wherein the first input clock signal and the second input clock signalare supplied from a DLL Delay Circuit.
 11. A semiconductor chipaccording to claim 9, wherein a period of the first logic level of thefirst input clock signal partially overlaps with that of the first logiclevel of the first input clock.
 12. A semiconductor chip according toclaim 8, wherein the second unit changes the first output clock signalfrom the first logic level to the second logic level when the secondinput signal is detected as being at the first logic level when thesecond input signal is detected as being at the first logic level at atime of detection of the change of the first input signal and when thefirst logic level of the first input clock signal is detected at a timeof detection of the change of the second input clock signal form thesecond logic level to the first logic level.